1. Field of the Invention
The present invention relates to a drive control apparatus for a vehicle, employed for following another vehicle which is preceding ahead.
Priority is claimed on Japanese Patent Application No. 2003-99122, filed Apr. 2, 2003, the content of which is incorporated herein by reference.
2. Description of Related Art
A drive control apparatus for a vehicle (a first vehicle) is known in which a preceding vehicle (a second vehicle which runs ahead of the first vehicle) which the first vehicle should follow is detected by a preceding vehicle detecting means such as a radar, an image sensor, etc., a distance to the preceding vehicle and a relative velocity with respect to the preceding vehicle are calculated, and, depending on such information, an inter-vehicle distance between the first vehicle and the preceding vehicle is controlled so that interference therebetween is avoided. In such a drive control apparatus, when the vehicle is placed in a control state, the preceding vehicle is detected, a signal indicating the preceding vehicle is sent to the driver of the first vehicle, and a control operation of the inter-vehicle distance between the first vehicle and the preceding vehicle is executed. On the other hand, when the vehicle is switched into a non-control state, the control operation of the inter-vehicle distance is suspended, and sending of the signal indicating the preceding vehicle is also suspended (see, for example, Japanese Unexamined Patent Application, First Publication No. 2001-63401).
As described above, in the known technological means, because the drive control apparatus for a vehicle executes the control operation of the inter-vehicle distance with respect to the preceding vehicle while sending information indicating detection of the preceding vehicle to the driver of the first vehicle, which is following the preceding vehicle, and the driver of the first vehicle can grasp the positional relationship between the preceding vehicle and the first vehicle during the control operation of the inter-vehicle distance, the driver entrusts driving of the vehicle to the drive control apparatus at ease under normal conditions; however, due to bad road conditions, a problem may be encountered when the driver cannot visually understand the environment.
More specifically, when, for example, the vehicle in which the drive control apparatus is installed runs on a snowy road or runs in falling snow, visibility to the driver in the vehicle following the preceding vehicle may be significantly reduced due to snow flung up from the road or by falling snow. On the other hand, because a radio wave type radar, such as a millimeter radar, has excellent environmental robustness, and the wave type radar can reliably detect a preceding vehicle even when snow as an obstacle exists between the first vehicle and the preceding vehicle, the control operation of the inter-vehicle distance with respect to the preceding vehicle can be executed.
However, because the preceding vehicle cannot be clearly seen due to reduction of visibility, the driver may suspend the control operation of the inter-vehicle distance by the drive control apparatus, and may try to manually maneuver the vehicle. In this state, even though the control operation of the inter-vehicle distance by the drive control apparatus is suspended by the driver's intention, the driver may wish to obtain information indicating existence of a preceding vehicle under such conditions of reduced visibility.
In the case of the known drive control apparatus, because the control operation of the inter-vehicle distance by the drive control apparatus must be executed in order to obtain information regarding the preceding vehicle, a problem is encountered in that the driver's intention to suspend the control operation of the inter-vehicle distance by the drive control apparatus and to manually maneuver the vehicle is incompatible with the driver's intention to obtain information regarding the preceding vehicle.